Liquid cargo transport ships include a MOSS type LNG transport ship which stores a LNG (liquefied natural gas) in a spherical tank and transports the LNG. In such a transport ship, the temperature of the cargo stored in the tank is extremely low (about −163 degrees centigrade). In order to prevent the temperature of a hull itself from significantly decreasing by this cargo, the tank is supported by the hull via a tank skirt.
Typically, the hull is made of iron-based steel in order to secure its strength, and the tank is made of an aluminum alloy in order to resist low temperature. The tank skirt is interposed between these dissimilar metal materials and includes a tank supporting member made of the same material as the tank and fixed to the tank and a hull supporting member made of the same material as the hull and fixed to the hull. These supporting members are joined to each other by a dissimilar joint structure.
Patent Document 1 discloses the dissimilar joint structure including a first plate-shaped member joined to an end portion of the tank supporting member and a second plate-shaped member joined to an end portion of the hull supporting member. In accordance with this dissimilar joint structure, an end surface of the first plate-shaped member and an end surface of the second plate-shaped member are caused to face each other, and these facing portions are joined to each other by friction stir welding. As compared to a case where explosive cladding is utilized, by utilizing the friction stir welding, the dissimilar joint structure can be increased in length, and a projection length of the dissimilar joint structure with respect to both supporting members can be decreased.
Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2007-153064